Multilayer electronic circuitry requires that there be electrically conductive interconnective holes or vias between layers. With the growing demand for higher density circuits, there has been an increased need for the vias to be smaller, on the order of 1 mil or less. The usual method for making vias has been to drill holes in a metal-clad dielectric substrate, clean the debris from the hole, etch back the substrate, deposit a thin layer of metal electrolessly on the hole walls, and electroplate metal (usually copper) over this to the desired thickness. This process suffers from the disadvantage that it is limited by the size of available drills and therefore cannot produce holes of less that 3 or 4 mils in diameter. Small diameter drills also are not very durable and tend to dull and break easily.
In a second method, a focussed laser beam is addressed to the spot on a dielectric substrate where a via is desired and the substrate ablated away down to the desired depth. Again the hole may be plated up or filled with a conductor to provide electrical interconnection if necessary. Some small vias can be made this way, but the technique works best on holes of about 5 mils or larger in diameter. In addition, there can be debris left around the hole which needs to be cleaned and the technique can be very slow for a large array of fine holes.
It is therefore an object of the present invention to provide a process for defined etching substrates whereby the etched features can be very small, whereby a large number of features can be made simultaneously, and whereby multiple etching steps are not required.
While the process of the invention is particularly suited for use with insulating substrates for electronic applications, it will be recognized that the process is also suitable for use with other substrates, e.g., metals, conductive films, etc.
Furthermore, while the process of the invention is particularly suited for making small holes and vias for interconnects in electronic circuitry, it is also suitable for etching wells or grooves or cut lines for defining or separating a part.